This invention relates to novel resistor elements which have good high temperature stability and long life as potentiometer resistor elements. Here, "good high temperature stability" means small change in electrical resistivity when the resistor elements are stored at high temperature. And, "long life" also means small change in electrical resistivity when the resistor elements are used in potentiometers.
Composition film resistors comprising resistor films and insulating substrates are widely used as fixed or variable resistors. And, for long life potentiometers, so-called conductive plastics wherein the resistor films 1 and insulating substrates 2 are molded together as shown in FIG. 1 are used.
In conductive plastics, phenolic resins, xylene resins, or diallyl phthalate resins were used as binders of resistor films and substrates. Although these resins are satisfactory for conventional uses, they are not satisfactory for special purposes such as automotive electronics where high temperature stability and long life is expected.
For the purpose of only improving thermal stability, the combination of ceramics or polyimide substrates and resistor films using aromatic polyimide resin as binders suffices. But, in this case, revolution life is a maximum 5.times.16.sup.6 revolutions, and that is insufficient for long life potentiometers.
An object of this invention is, therefore, to provide novel thermally stable and long life resistor elements for potentiometers.